1. Field of the Invention
A CD-ROM containing a computer program listing appendix has been submitted. The CD-ROM contains 1 dick, containing a total of 218 files.
The present invention is broadly concerned with an improved material transition analyzer and method permitting analysis of non-uniform, composite materials in order to determine temperature-related phases of material, such as the glass transition temperature (Tg) and melt transition temperature (Tm). More particularly, the invention is concerned with such analyzer and method wherein the analyzer includes a body having a sample chamber, a sample heating assembly, and a force-applying assembly operable to apply a compressive force to the sample which decreases the chamber volume in response to sample phase changes; the change in volume is detected, preferably by monitoring corresponding shifting of a portion of the force-applying assembly.
2. Description of the Prior Art
Thermal processing techniques such as extrusion and pelleting generate complex chemical and physical changes in ingredients to produce final products with desired characteristics. Modern instruments and analytical tools can measure these often minute but critical changes. By correlating these changes to desired properties in finished products, it is possible to predict processing effects and to more accurately formulate diets and automated processing parameters.
A relatively new approach that is rapidly increasing in popularity is the application of polymer science to extrusion and similar technologies. Having roots in the plastic polymer industry, polymer science can be used to study the physical changes associated with glass transition and melt transition in biopolymers such as starches and proteins. In order to make use of the principles of polymer science, it is first important to recognize the difference between the crystalline physical state and the amorphous (noncrystalline state). In basic terms, if the polymers in a substance become very ordered, they interact with one another and form a crystalline structure. In amorphous materials, adjacent strands of the polymer do not interact with one another and, therefore, do not crystallize. It is important to understand that the principles of polymer science apply only to amorphous materials.
Both synthetic and food polymers often exist in an amorphous or partially amorphous state. These amorphous compounds undergo both glass transition and melting at characteristic temperatures Tg and Tm, respectively. When the temperature of the compound is above Tg but below Tm, it is easily deformed but is not so liquid-like that it flows, and the compound is considered xe2x80x9crubberyxe2x80x9d or leathery.
An example of a rubbery material is a food product as it exits an extruder before cooling and drying. At this point in the process, the crystalline starch structure has been destroyed, and the mass is amorphous. When grasped by hand, the product can be easily deformed without fracturing the structure, yet it is sufficiently coherent that it will not flow through one""s fingers.
When the temperature of a compound is below Tg, it is considered xe2x80x9cglassyxe2x80x9d. An example of a glassy material is an extruded food product after it has been dried or, in some cases, only cooled. At this point, the structure is amorphous, and when deformed with one""s fingers, the structure fractures.
When the temperature of a compound is above Tm, its properties are fluid-like, and the compound is considered xe2x80x9cmelted.xe2x80x9d An example of a melted material is extrudate that is heated and plasticized sufficiently to flow through the extruder die.
Important changes in the physical properties of polymers occur as they pass through their glass transition temperatures. The most notable changes occur in molecular mobility, viscosity, and elasticity.
In the rubbery state, molecular mobility, indicated by the material""s viscosity, is much, much greater than in the glassy state. Therefore, in the rubbery state, viscosity is much, much lower than in the glassy state. For example, the viscosity of a glassy material may be in the range of 1012 Pa while the corresponding viscosity of the same material in the rubbery state would be several orders of magnitude less. Similarly, several order-of-magnitude differences in viscosity can be seen between the rubbery state (Tm less than T less than Tg) and the melted state (T greater than Tm). See, Zhang et al., Factors Affecting Expansion of Corn Meals with Poor and Good Expansion Properties, Cereal Chemistry, Vol. 75, No. 5, (1998); and Strahm, Fundamentals of Polymer Science as an Applied Extrusion Tool, Cereal Foods World, Vol 43, No. 8, (1998).
Devices have been proposed in the past to measure the properties of grain products at or near the pressures and temperatures encountered in high-temperature short-time extrusion, Zhang et al., Capillary Rheometry of Corn Endosperm: Glass Transition, Flow Properties, and Melting of Starch, Cereal Chemistry, Vol. 75, No. 6, (1998). The Zhang et al. device makes use of a capillary block with opposed, constant volume chambers on opposite sides of the block. Each chamber contained a piston which were moved together through sidebars ensuring that the volume of the chambers remained constant while preventing moisture loss through the atmosphere.
The present invention provides an improved phase transition analyzer comprising a body having a chamber presenting an open end and adapted to receive a material sample, together with a heating assembly for controllably heating a sample within the chamber and a force-applying assembly operable to apply a compressive force to the sample with the chamber during heating thereof. The force-applying assembly includes a block adjacent the open end of the body which at least substantially closes the chamber to inhibit flow of the sample therefrom. The force-applying assembly is operable to decrease the volume of the chamber in response to changes in the sample arising from heating and application of force thereto. A device is also provided to determine the decrease in volume of the chamber, which is used to denote a material phase change. In preferred forms, a portion of the force-applying assembly is shiftable in response to changes in the sample, and the device determines the shifting of the force-applying assembly portion.
In preferred forms, the analyzer body comprises an elongated, tubular member which receives an elongated stationary rod, and the block is coupled with a drive unit for urging the block in a direction to compress the sample between the block and the inner end of the rod. In this way, the material sample is subjected to heating and compaction forces so that, when a phase change occurs, the volume of the sample chamber is decreased and detected.
In order to most easily analyze for Tgand Tm, the block is preferably a shiftable member having a solid or blank portion and a spaced second portion provided with a capillary opening therethrough. In use, a sample is loaded into the chamber, with the latter closed in its first position, and a compressive force is exerted on the sample while the latter is heated at a predetermined rate; when the material reaches its Tg, the sample contracts and the chamber volume correspondingly decreases, the latter being detected. Thereafter in order to measure Tm, the block is shifted to its second position and the sample is again heated while being subjected to a compressive force. When the Tm is reached, a portion of the sample flows through the block capillary opening, again causing a detectable decrease in chamber volume.